I've heard ear tones all my life and always wondered what it could be. I would say it resembles a high pitched tone similar to what you hear during a hearing test. A I got older I first thought there was a problem, but soon realized thatit went away fairly quickly. Since becoming an engineer,, and knowing a little about frequency modulation,, I came to think that I was some how picking up on electronic equipment generating a tone,, or even electromagnet waves. I still don't know,, maybe the aliens are broadcasting on my wavelength? :-)